Millimeter wave device and method of making

ABSTRACT

A method for making a millimeter wave device having a dielectric substrate with a pair of substantially parallel planar surfaces with at least one predetermined millimeter wave circuit pattern formed in a conductive layer located on at least one of the substrate surfaces. A substantially planar conductive channel plate is mounted adjacent the conductive layer on one substrate surface with the channel plate having an aperture overlying each circuit pattern formed in the conductive layer. A substantially planar conductive cover plate is mounted adjacent one of the channel plates so as to form a first cavity in the region defined by the substrate surface, the channel plate aperture and the cover plate. The device may further include a second substantially planar conductive channel plate mounted adjacent the other one of the substrate surfaces with the second channel plate having an aperture corresponding to and aligned with the first channel plate aperture. A second substantially planar conductive cover plate is mounted adjacent the second channel plate so as to form a second cavity in the region defined by the other substrate surface, the second channel plate aperture and the second cover place. A substantially planar conductive back place may be mounted adjacent each cover plate to provide support to the device structure. For the production of large quantity, high yield devices, the channel places, cover plates, and back plates are fabricated by photolithography with chemical milling, to achieve device high performance operation. Alternatively the channel plates and back plates are integrally formed by combining photolithography and electroforming techniques.

This is a continuation of application Ser. No. 07/739,205, filed Jul.30, 1991, now abandoned, which was a Divisional of application Ser. No.07/112,330, filed Oct. 23, 1987, now U.S. Pat. No. 5,062,149.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to millimeter wave device structures andmethods of making. More specifically, the present invention relates to anovel and improved millimeter wave device featuring a sandwich-typeconstruction and methods of accurate, high throughput manufacture.

II. Background Art

Current state-of-the-art millimeter wave devices for operating atfrequencies employing signals having a wavelength of one to tenmillimeters are traditionally constructed in metal waveguide. Typicalconstruction techniques implement the traditional dimensional milling ofthe metal structure. However, since the waveguide dimensions areproportional to the operating wavelength, these dimensions becomesmaller as the frequency increases. As the frequency of the deviceincreases, the complexities of traditional fabrication and the stricttolerances required become extremely difficult to achieve. In largequantity production schemes, traditional precision milling techniquesare extremely cost prohibitive in achieving the precision required fordevices in all types of applications.

In an attempt to solve problems of yield, size and weight associatedwith millimeter wave device structures which are required to provideperform at frequencies in excess of 100 GHz, several alternate methodsof constructing transmission lines and circuits have been employed.

Millimeter wave devices are typically manufactured in microstrip,coplanar waveguide and slot line structures. However, millimeter wavedevices manufactured as microstrip, coplanar waveguide and slot linestructures are not practical due to the high losses encountered atfrequencies above 60 GHz.

Another approach in fabricating millimeter wave devices is constructingthe device in a dielectric image guide structure. However, intolerablelevels of radiation and scattering are generated in the dielectric imageguide structures. The undesirable effects in these structures are theresult of discontinuities caused by devices such as ferrites and diodescontacting the dielectric lines. Of these structures, microstrip,coplanar waveguide, slot line and dielectric image guide, none offer thehigh performance required in millimeter wave devices which operate atfrequencies in excess of 100 GHz.

Alternate structures for millimeter wave devices have utilized finlineor suspended strip line. In these types of structures, transmissionlines and mixers have shown good performance at the higher millimeterwave frequencies. However, other components manufactured in thesestructures have had less than successful performance. The limitationsupon finline and suspended strip line structures are a result of preventconstruction techniques. These techniques require high precisionmachining of air channels along with critical positioning of thesubstrate and ground surfaces. The requirement of high precisionmachining pose significant problems in large quantity manufacturing,especially on a cost-effective basis.

Overall, in the area of millimeter wave devices operating at frequenciesin excess of 70 GHz, little activity in developing accurate devicesadaptable to a low cost, high volume production process has beenundertaken. A major reason for lack of activity in this area is due tothe complexity of fabrication of these high frequency devices. Theimplementation of the usual fabrication techniques for millimeter wavedevices typically results in poor electrical high frequency performance.Implementation of standard manufacturing techniques in the manufactureof millimeter wave devices, which is only hoped to achieve satisfactoryoperating characteristics, has projected production costs which arehighly excessive in high quantity production runs. Therefore, millimeterwave device usage in large scale programs has been quite limited mainlydue to technical difficulties, cost prohibitions of large quantityproduction, and lack of reproduction accuracy in unit performance.

It is therefore, an object of the present invention to provide a noveland improved high performance millimeter wave device and method ofmanufacture.

It is yet another object of the invention to provide a method forfabricating high performance millimeter wave integrated circuit devicesutilizing high volume fabrication techniques.

SUMMARY OF THE INVENTION

Our invention consists of a millimeter wave device having a dielectricsubstrate with a pair of substantially parallel planar surfaces with atleast one predetermined millimeter wave circuit pattern formed in aconductive layer located on at least one of the substrate surfaces. Asubstantially planar conductive channel plate is mounted adjacent theconductive layer on one substrate surface with the channel plate havingan aperture overlying each circuit pattern formed in the conductivelayer. A substantially planar conductive cover plate is mounted adjacentone of the channel plates so as to form a first cavity in the regiondefined by the substrate surface, the channel plate aperture and thecover plate. The device may further include a second substantiallyplanar conductive channel plate mounted adjacent the other one of thesubstrate surfaces with the second channel plate having an aperturecorresponding to and aligned with the first channel plate aperture. Asecond substantially planar conductive cover plate is mounted adjacentthe second channel plate so as to form a second cavity in the regiondefined by the other substrate surface, the second channel plateaperture and the second cover plate. A substantially planar conductiveback plate may be mounted adjacent each cover plate to provide supportto the device structure. For the production of large quantity, highyield devices, the channel plates, cover plates, and back plates arefabricated by precision techniques such as by photolithography withchemical milling, or electrodischarge machine wire saw fabricationtechniques to achieve device high performance operation. In an alternateembodiment of the invention the channel plates, cover plates and backplates are integrally formed by combining photolithography andelectroforming techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, objects and advantages of the presentinvention will be more fully apparent from the detailed description setforth below taken in conjunction with the drawings in which likereference characters identify correspondingly throughout and wherein:

FIG. 1 is a block diagram of an exemplary millimeter wave integratedcircuit transceiver;

FIG. 2 is a perspective view of the exemplary embodiment of themillimeter wave transceiver of FIG. 1, constructed in accordance withthe present invention, with the transceiver being separated forillustrative purposes;

FIG. 3 is a side elevation view of the millimeter wave transceiver ofFIG. 2;

FIG. 4 is a top plan view of the millimeter wave transceiver of FIG. 2;

FIG. 5 is a bottom plan view of the millimeter wave transceiver of FIG.2;

FIG. 6 is a side sectional view taken across line 6--6 of the millimeterwave transceiver of FIG. 4;

FIG. 7 is a side sectional view taken across line 7--7 of the millimeterwave transceiver of FIG. 4;

FIG. 8 is a top plan view of the circuit board employed in themillimeter wave transceiver of FIG. 2;

FIG. 9 is a bottom plan view of the circuit board employed in themillimeter wave transceiver of FIG. 8;

FIG. 10 is a perspective view of a fixture holding a plurality of airchannel plates, partially cut away for illustrative purposes;

FIG. 11 illustrates the processing steps in fabricating millimeter waveintegrated circuit housing components;

FIG. 12 illustrates alternate processing steps in fabricating millimeterwave integrated circuit housing components;

FIG. 13 illustrates an alternate process for forming a millimeter waveintegrated circuit device housing;

FIG. 14 illustrates an alternate process for forming a millimeter waveintegrated circuit device housing; and

FIG. 15 illustrates an alternate process for forming a millimeter waveintegrated circuit device housing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention comprises a novel and improved millimeter wavedevice and methods of making. Referring to FIG. 1, there is shown anexemplary block diagram of a millimeter wave transceiver 10. Thetransceiver of FIG. 1 is but one example of the many types of millimeterwave circuits and the various millimeter wave components which may bemanufactured using the construction techniques disclosed herein.

The block diagram of FIG. 1 illustrates the basic function of amillimeter wave frequency modulated continuous wave (FMCW) integratedcircuit transceiver 10. In transceiver 10, modulated DC power is appliedto bias filter 12 which filters out unwanted AC frequency components andnoise from the input DC power. DC power from bias filter 12 is coupledto transmitter 14, which is typically a GUNN diode. The level of the DCvoltage provided by the DC power source determines the frequency ofoscillation of the GUNN diode. The electromagnetic energy generated bytransmitter 14 is coupled through a duplexer or circulator 16.Circulator 16 is used to couple the energy to an antenna (not shown)typically through a waveguide port in the transceiver housing.

In the receiving mode, electromagnetic energy is coupled into thetransceiver from the antenna through the waveguide port to circulator16. Circulator 16 channels the received electromagnetic energy to mixer18. Mixer 18 mixes the beat frequencies of the received millimeter wavesignal. The low frequencies of the mixed signal are then coupled throughIF filter 28 to an IF demodulator (not shown).

FIG. 2 illustrates by perspective view the exemplary millimeter wavetransceiver of FIG. 1 with the transceiver being separated and certaincomponents removed for purposes of illustration. Components notspecifically identified by reference numerals in FIG. 2 are furtherillustrated in FIGS. 3-7. In FIG. 2, transceiver 10 is configured aboutcircuit board 22 which consists of dielectric substrate 24 and aconductive layer formed on at least one of the surfaces of substrate 24.Circuit board 22 as illustrated in FIG. 2 has substrate 24 withconductive layer 26 formed on a substantially flat upper surface 28thereof. Substrate 24 also has a substantially flat bottom surface 30that is parallel to surface 28. A number of predetermined millimeterwave circuit patterns may be formed in conductive layer 26 as describedfurther herein.

Positioned against circuit board 22 are a pair of substantially flat airchannel plates or shims 32 and 34. Positioned against conductive layer26 formed on upper surface 28 is air channel shim 32. Positioneddirectly against lower surface 30 is air channel shim 34. Air channelshims 32 and 34 each has an air channel aperture formed therein tosupport millimeter wave propagation along circuit patterns formed on thecircuit board. For example, air channel shim 32 includes air channelaperture 36. Air channel shims 32 and 34 also contain holes therethroughwhich provide the necessary feedthrough for components and connectors tothe circuit board. Air channel shims 32 and 34 also contain additionalholes for alignment and mounting purposes as discussed later.

Respectively mounted adjacent air channel shims 32 and 34 aresubstantially flat cover plates or shims 38 and 40. Cover shims 38 and40 overlie the respective air channel shims 32 and 34 so as to formenclosed cavities in the air channel aperture regions. Holes areprovided through cover shims 38 and 40 to provide component placement,through the stack of cover shims and air channel shims, into thecavities region. Additionally, holes are provided in cover shims 38 and40 for alignment purposes.

A pair of substantially flat back plates 42 and 44 are respectivelymounted adjacent cover shims 38 and 40. Back plates 42 and 44 are usedto provide structural rigidity to the transceiver. Back plates 42 and 44are typically substantially thicker than the air channel shims and covershims. Back plates 42 and 44 provide structural support to thetransceiver to permit attachment of the device to other structures, inaddition to the mounting of external structures, such as waveguides, tothe device. Back plates 42 and 44 also provide the necessary support forthe mounting of components within the transceiver itself.

A GUNN diode mounting fixture 46 (FIG. 7) is mounted in threaded hole 48which extends through back plate 42 from a top surface to a bottomsurface that is adjacent cover shim 38. Mounting fixture 46 (FIG. 7)makes electrical contact to backplate 42 and one terminal of the GUNNdiode (diode 144 of FIG. 7) (FIG. 7). The other terminal of the diode,coupled to pin 47, (FIG. 7) extends through an aligned hole 50 in covershim 38, and into air channel aperture 36. The GUNN diode (diode 144 ofFIG. 7) has one terminal connected to mounting fixture 46 that iselectrically connected to backplate 42 and the other terminal contactingthe printed circuit pattern formed in conductive layer 26 on uppersurface 28 of circuit board substrate 24.

Extending through the aligned holes in back plate 42 and cover shim 38,respectively threaded hole 52 and hole 54, into the air channel aperture36 adjacent the circuit pattern formed in layer 26, is a ferrite rod 56(FIG. 7). A cylindrical shaped magnet 58 (FIG. 7) having either aclockwise or counterclockwise polarization defined about a centrallongitudinal axis is mounted directly opposite and aligned with theferrite rod in hole 60 in back plate 44. Ferrite rod 56 and magnet 58function as a circulator in transceiver 10.

A waveguide port is configured as a series of rectangularly shapedaligned holes which alignedly extend through back plate 42 and covershim 38, respectively as hole 62, and intersect with an alignedrectangularly-shaped end of air channel aperture 36. Similarly,rectangular-shaped holes, holes 66, symmetrically aligned with hole 62extend respectively through back plate 44 and cover shim 40 where itintersects with an aligned rectangular-shaped end of air channelaperture 70. A back short tuner 72 (FIG. 3) is mounted in transceiver 10through holes 66 and into air channel aperture 70 if necessary.

A coaxial connector 74 (FIG. 6) is mounted in threaded hole 76 in backplate 44 and has a center conductor 75 which extends through an alignedhole 78 in cover shim 40, air channel aperture 132 and through hole 80in circuit board 22 so as to electrically connect to a mixer circuitpattern formed in conductive layer 26. Connector 74 couples the IFfrequency, provided by a mixer circuit pattern and a mixer diode fromthe received millimeter wave frequencies, external to transceiver 10.

Mounted in hole 82 in back plate 44 is connector 84 (FIG. 3). Pin 86centrally mounted in connector 84 electrically isolated from theconnector housing. Pin 86 extends through aligned hole 88 in cover shim40, air channel aperture 128, and through hole 90 in circuit board 22where it connects to a bias filter circuit pattern on conductive layer26. Externally applied DC power provided to pin 86 is coupled throughthe bias filter circuit pattern to the GUNN diode with mounting fixture46 connected to DC power ground.

A pair of alignment pins 92 (FIG. 4) are mounted in back plate 42 andextend through aligned openings 94 through cover shim 38, air channelshim 32, circuit board 22, air channel shim 34 and cover shim 40 wherethey mate in holes 94 in back plate 44. These alignment pins keep thecircuit board cover shims, air channel shims and back plates inalignment for precise positioning of components, holes and air channelapertures.

In the exemplary embodiment of transceiver 10, the structure isconfigured in a substantially square orientation. The transceiversandwich-like structure is held together in position by screws 96 whichextend through the structure near each corner. Bolts 96 (FIG. 7) extendthrough aligned holes, countersunk holes 98 in back plate 42, holes 100,cover shim 38, air channel shim 32, circuit board 22, air channel shim34, cover shim 40 where they engage in the aligned threaded holes 102 inback plate 44.

FIGS. 3, 4 and 5 respectively illustrate side elevation, top plan andbottom plan views of the transceiver of FIGS. 1 and 2. Referring to FIG.3, in addition to FIG. 2, circuit board 22 is sandwiched between airchannel shims 32 and 34 with air channel shim 32 being mounted adjacentconductive layer 26. Air channel shims 32 and 34 are respectivelysandwiched between cover shims 38 and 40 with circuit board 22 disposedbetween air channel shims 32 and 34. Similarly, cover shim 38 and 40 arerespectively overlaid by back plates 42 and 44.

Back short tuner 72 is mounted in back plate 44 and extends thereinthrough holes 66 and hole 66 in cover shim 40. Back short tuner 72extends into air channel aperture 70. Coaxial connector 74 is alsomounted in back plate 44. Connector 74 has a center pin 75 which iselectrically insulated from the connector housing. Pin 75 extendsthrough hole 78 in cover shim 40, air channel aperture 132 and hole 80in circuit board 22 to make electrical contact only with a circuitpattern in layer 26. Also mounted in back plate 44 is magnet 58 which isa cylindrically shaped magnet snaring a common longitudinal axis withferrite rod 56. Connector 84 is also mounted in back plate 44 with pin86 extending through hole 88 in cover shim 40, air channel aperture 128and hole 90 in circuit board 22 to make electrical contact with acircuit pattern in layer 26.

FIG. 4 illustrates a top plan view of transceiver 10 and is to beconsidered with reference to FIG. 2. In FIG. 4, screws 96 are positionedwith their head in countersunk holes 98. Screws 96 extend through holes100 in the transceiver structure and are threadably engaged in themating threads of holes 102 formed in back plate 44. Screws 96 areutilized to hold together the sandwiched structure of transceiver 10.Mounting holes 104 extend through each of the layers of the sandwichedtransceiver structure to facilitate mounting to and with externalstructure.

A waveguide port is formed by the aligned rectangularly shaped holes 62which respectively extend through back plate 42, cover shim 38. Holes 62align with a similar rectangularly shaped end of air channel aperture36. Electromagnetic energy is coupled in and out of the transceiverstructure through this waveguide port which may be attached to anantenna (not shown). The waveguide port is electromagnetically coupledto the transceiver components by transmission line 106, which is a wellknown microwave circuit pattern that is etched in conductive layer 26.Transmission line 106 extends along substrate 24 where it intersectswith other circuit patterns in the region beneath hole 54.

In the particular embodiment illustrated herein the transceivercirculator is comprised of a circuit pattern in conductive layer 26,ferrite rod 56 and magnet 58. Ferrite rod 56 is threadable mounted inhole 52 in back plate 42 and extends into the transceiver structurethrough hole 54 in cover shim 38 into a cavity defined by the walls ofair channel aperture, cover shim 38 and circuit board 22. The end offerrite rod 56 is spaced apart from and overlies a printed circuitpattern formed in conductive layer 26. Air channel aperture 36 is of aY-shaped configuration with the ferrite rod 56 positioned at theintersection of the three aperture legs, legs 108, 110 and 112.

Leg 108 overlies a transmission line circuit pattern formed inconductive layer 26. Leg 110 overlies an oscillator circuit patternformed in conductive layer 26. Leg 112 overlies a mixer circuit patternformed in conductive layer 26.

At the outward end of leg 108, the end opposite the intersection of legs108, 110 and 112, is the opening for the waveguide port. Along leg 110,near the outward end thereof, GUNN diode mounting fixture 46 extendsthrough the aperture leg.

Between the intersection of legs 108, 110, and 112 and the outward endof leg 110 a keyhole-shaped aperture 114. Aperture 114 extendssubstantially perpendicular from leg 110 and is connected thereto by athin channel aperture 116. Aperture 114 overlies the bias filter circuitpattern formed in conductive layer 26. Between the intersection of legs108, 110 and 112 and the outward end of leg 112 is another keyholeshaped aperture 118. Aperture 118 extends substantially perpendicularfrom leg 112 and is connected thereto by a thin channel aperture 120.Aperture 118 overlies the IF filter circuit pattern formed in conductivelayer 26.

FIG. 5 illustrates a bottom plan view of transceiver 10 and is to beconsidered with FIG. 2. In FIG. 5, screws 96 are threadably engaged inholes 102 in back plate 44 for rigidly retaining together the sandwichstructure of transceiver 10. Magnet 58 is secured in hole 60 in backplate 44 by means well known in the art. Magnet 58 is aligned on acommon longitudinal axis with ferrite rod 56. Air channel aperture 70 isformed in air channel shim 34 and is identical in shape, and orientationin the transceiver as is aperture 36.

Aperture 70 has Y-shaped configuration with legs 122, 124, and 126extending from a center intersection of the legs. In the sandwichstructure of transceiver 10, air channel aperture 70 is aligned with airchannel aperture 36 such that legs 122, 124 and 116 respectively alignwith legs 108, 110 and 112. Legs 122, 124 and 126 extend outwardly in aY-shaped configuration from the center intersection of the legs. Thecenter intersection of the legs is located above magnet 58.

Leg 122 extends outwardly from the intersection of legs 122, 124 and 126where at its end it has a rectangular shape so as to align with hole 66.Back short tuner 72 is mounted in hole 66 and extends into leg 122. Leg124 extends outwardly from the intersection of legs 122, 124 and 126.Between the end of leg 124 and the intersection of legs 122, 124, leg124 a keyhole-shaped aperture 128 is formed. Aperture 128 extendssubstantially perpendicular to leg 124 and is aligned with aperture 114in the transceiver structure. Aperture 128 is connected to leg 124 bychannel 130. Similarly, leg 126 extends outwardly from the intersectionof legs 122, 124 and 126. Between the end of leg 126 and theintersection of legs 122, 124 and 126, a keyhole-shaped aperture 132 isformed. Aperture 132 extends substantially perpendicular to leg 126 andis aligned with aperture 118 in the transceiver structure. Aperture 132is connected to leg 126 by channel 134.

Bias filter connector 84 is mounted in back plate 44 such that pin 86extends through the region defined by aperture 128. Similarly, coaxialconnector 74 is mounted in back plate 44 such that pin 75 extendsthrough the region defined by aperture 132.

FIG. 6 illustrates the transceiver in a sectional view with a crosssection taken along line 6--6 of FIG. 4. Back plates 42 and 44 inconjunction with mounting screws 96 clamp with uniform pressure thesandwiched cover shims 38 and 40, air channel shims 32 and 34 andcircuit board 22. Back plates 42 and 44 are flat plates typically in therange of 0.1-0.2 inches in thickness and are constructed of a rigidconductive metal such as brass.

Cover shim 38 is mounted adjacent back plate 42 and overlies air channelshim 32. Similarly, cover shim 40 is mounted adjacent back plate 44 andoverlies air channel shim 34. Cover shims 38 and 40 are flat platestypically in the range of 0.003-0.005 inches in thickness and areconstructed from a conductive metal such as brass. Cover shim 38 acts asa top wall or cover for apertures 36, 114, and 118 of air channel shim32. Cover shim 40 acts as a bottom wall for apertures 70, 128, and 132of air channel shim 34. Cover shim 40 includes hole 88 through which pin86 of bias connector 84 extends into aperture 128. Cover shim 40 alsoincludes hole 78 through which pin 75 of coaxial connector 74 extendsinto aperture 132.

Air channel shim 32 is mounted between cover shim 38 and conductivelayer 26, conductive layer 26 being mounted upon surface 28 of substrate24. Similarly, air channel shim 34 is mounted between cover shim 40 andsurface 30 of substrate 24. Air channel shims 32 and 34 are typicallyflat conductive metal plates typically in the range of 0.010 -0.025inches in thickness. The interior walls of the apertures formed in airchannel shims 32 surround printed circuit patterns formed in conductivelayer 26. The aperture width and position relative to the circuitpatterns is critical in maintaining an electromagnetic signal therein inthe TEM mode at the operating frequency the device. The height, orthickness, of air channel shims 32 and 34 control the characteristicimpedence of the overlain printed circuit pattern, at the millimeterwave frequencies. Therefore, the combination of cover shims 38 and 40respectively overlying air channel shims 32 and 34 define cavities inthe air space above a printed circuit pattern that is defined both interms of width and height. The width of each aperture is of a dimensionsufficient to maintain the wave propagated therein in a TEM mode at thecharacteristic impedence of the circuit pattern. The dimensional aspectsof the apertures are relatively well known by those skilled in the art.

Mounted between air channel shims 32 and 34 is circuit board 22. Circuitboard 22 is typically constructed of a 0.005 inch thick TEFLON, atrademarked waxy, opaque polytetrafluoroethlene, dielectric substrate 24with a layer of 1/2 ounce copper on both sides. As illustrated in FIG.6, the copper layer is illustrated as layer 26 on surface 28 ofsubstrate 24. The layer initially on surface 30 is substantially removedwith only pads 126 and 138 and portion 168 remaining. Pad 126 is coupledby plated-through hole 90 in substrate 24 to matching pad 140 of acircuit pattern formed in layer 26. Similarly, pad 138 is electricallyconnected through plated through hole 80 in substrate 24 to a matchingpad 142 of a different circuit pattern in layer 26. As illustrated inFIG. 6, pins 86 and 75 respectively electrically connect to pads 126 and138. Formed in layer 26 within the boundaries defined by the aperturesof air channel shims are circuit patterns which are described later indetail. Outside of the boundaries defined by the apertures of the airchannel shims, layer 26 is electrically separated from the circuitpatterns so as to function as a circuit ground plane.

FIG. 7 illustrates the transceiver in a sectional view with a crosssection taken along line 7--7 of FIG. 4. In FIG. 7, aligned holes 98,100 and 102 extend through the sandwich structure of the transceiver.Hole 98 is countersunk at the exterior surface of back plate 42 whilehole 102 is threaded in back plate 44. Bolt 96 extends through thestructure at hole 98, holes 100 and is threadedly engaged in hole 102 inback plate 44. The head of screw 96 fits within the countersunk regionof hole 96 at the exterior surface of back plate 42.

GUNN diode mounting fixture 46 is mounted in threaded hole 48 in backplate 42. One terminal of GUNN diode extends through hole 50 in covershim 38 and has GUNN diode 144 mounted at the end thereof. GUNN diode144 contacts the circuit pattern formed in layer 26 within leg 110 ofaperture 36. The diameter of hole 50 transforms the impedence of thediode to that of the circuit pattern which diode 114 contacts.

Ferrite rod 56 is threadedly mounted in hole 52 in back plate 42 andextends through an aligned hole 54 in cover shim 38. The end of ferriterod 56 is spaced above the center of the intersection of the legs of aY-shaped circuit pattern 146 (FIG. 2) that is formed in layer 26 onsurface 28.

The waveguide port is formed by the aligned rectangularly shaped holes62 which extends through back plate 42 and cover shim 38 into aperture36 at the outer end of leg 108. Back short tuner 72 is mounted inaligned rectangularly shaped holes 66 which are aligned with holes 62.Back short tuner extends in holes 66 through back plate 44, cover shim40 into air channel aperture 70 at the outermost end of leg 122.

A GUNN diode matching section is formed as cavity 148 which extends fromair channel aperture 70, at leg 124, through cover shim 40 and partiallyinto back plate 44. Hole 148 is aligned in the common longitudinal axisof pin 47 and acts as a oscillator matching section for GUNN diode 144.

Cover shim 40 prevents magnet 58 from falling into air channel aperturein addition to preventing the escape of millimeter wave energy aboutmagnet 58 positioned in hole 60. In certain structures a cover shimwould not be necessary when the back plate could serve the same functionas the cover shim.

FIGS. 8 and 9 respectively illustrate top and bottom views of circuitboard 22. Layer 30 is typically removed by photolithography and chemicaletching techniques well known in the art. These techniques are used toform millimeter wave circuit patterns on the circuit board. Asillustrated in FIG. 8, the basic circuit pattern is configured inY-shaped orientation with the circuit patterns being formed by each ofthe legs 150, 152 and 154. Additional circuit patterns 156 and 158respectively extend from legs 150 and 154. The circuit pattern formedwithin each leg is surrounded by gap 160 in the conductive layer whichexposes surface 28 of substrate 24. Gap 160 in the conductive layerprovides electrical isolation of the circuit patterns from thesurrounding conductive layer 26 which forms ground plane 162. Edge 164of ground plane 162 at the meeting of gap 160, is aligned with theinterior walls of the air channel apertures.

The circuit pattern formed within leg 154 includes at the outermost enda wide section which is positioned for contacting GUNN diode 144. Thecircuit pattern line narrows in width as it extends inwardly towards thecenter of the Y-shaped intersection of the legs 150, 152 and 154. Midwaybetween the end of leg 154 and the intersection of legs 150, 152 and 154the circuit pattern is electrically contacted by circuit pattern 158.Circuit pattern 158 is the bias filter circuit pattern, an LC and RCfilter combination with accompanying inter connect pad 140. Input DCpower is provided to a GUNN diode through this circuit pattern. Thiscircuit pattern inhibits the transfer of millimeter wave energy,generated in the transceiver, to pad 140 which is connected to the DCpower supply.

The circuit pattern formed by the intersection of legs 150, 152 and 154forms a circulator circuit in which ferrite rod 56 and magnet 58 aremounted on a common axis perpendicular to the plane of the surface oflayer 26. These components and the circuit pattern form the transceivercirculator.

Extending from the intersection of legs 150, 152 and 154 is the circuitpattern in leg 152 which is a strip of conductive layer 26. The circuitpattern of leg 152 terminates in the region near the end of leg 108 ofair channel aperture 36 beneath holes 62 in cover shim 38 and back plate42. The circuit pattern of leg 152 is transmission line 106 whichcouples millimeter wave energy between the waveguide port and thecircuit components.

Extending from the intersection of legs 150, 152 and 154 is the circuitpattern in leg 150. The strip of conductive layer 26 forming the circuitpattern of leg 150 is a mixer circuit pattern. The mixer circuit patternincludes mixer diode 170 coupled between the strip of conductive layer26 of the mixer circuit pattern and ground plane 162. At the endopposite the intersection of the circuit pattern legs, the circuitpattern strip of leg 150 is wide. The circuit pattern strip undergoes atransition to a narrow strip approaching the leg intersection. At thetransition area in the width of the circuit pattern near the end of leg150, mixer diode 170 is mounted along the narrow strip portion. Also inthe transistion area low pass filter circuit pattern 156 intersects themixer circuit pattern in leg 150. Millimeter wave frequencies reflectedalong the mixer circuit pattern are such that the reflected or beatfrequencies include low frequencies which are permitted to pass throughthe filter circuit pattern 156 to pad 142. The signal is coupled betweenpads 142 and circuit pattern 156 by plated-through hole 80 for couplingexternal to the transceiver by coaxial connector 74.

On leg 150 between the intersection of circuit pattern 56 and theintersection of legs 150, 152 and 154 there is a gap, gap 166, in theconductive layer. Gap 166 provides DC power isolation, of the DC powerprovided to GUNN diode 144. This DC power is present on the circuitpatterns on legs 152 and 154. However, in conjunction with a FIG. 9, aconductive strip 168 on surface 30 overlays gap 166. Strip 168 acts as atransformer for coupling millimeter wave energy from the mixer diodecircuit to the remaining circuit patterns in legs 152 and 154.

An exemplary embodiment of the frequency modulated continuous wavetransceiver is typically 1.0 inch by 1.0 inch along the sides with athickness of 0.25 inches. The transceiver has a volume of 0.25 cubicinches and a weight of 22 grams. An exemplary unit operates at anaverage power of 35 milliwatts with a frequency deviation of 50 MhZ. Atthe rated levels a noise figure of 15 dB at a modulation frequency of 2KhZ is typical. It is envisioned that a varactor-tuned GUNN diodetransmitter may be constructed so as to permit lower noise figures and alarger tuning range.

In the exemplary embodiment, circuit patterns were formed in aconductive layer basically only on a single side of the substrate.However, circuit patterns may be fabricated on both surfaces withcorresponding air channel aperture and component layout.

One method of fabricating the back plates, cover shims and air channelshims is by utilizing a wire electrode discharge machine (EDM). The EDMwire saw is typically threaded through a pre-drilled hole in one of themetal plates and cuts the metal via a spark gap. For high precisioncutting, a numerically controlled table may be used to move the partrelative to the cutting wire. The use of the EDM wire saw is especiallyvaluable for precision cutting of multiple pieces in predeterminedpatterns with high accuracy and reproducability. The EDM wire saw may beused to form the back plates, cover shims and air channel shims.

FIG. 10 illustrates fixture 200 having a top plate 202 and a bottomplate 204 secured together by screws 206. Stacked and clamped betweenplates 202 and 204 are a plurality of metal plates 208. A portion ofsome of metal plates 208 are cut away for purposes of illustrating thecutting action of EDM wire saw cutting wire 210.

Plates 202 and 204 act as a template that typically have predeterminedaperture patterns previously formed therein, to prevent redundantcutting of the fixture plates. Holes are also pre-drilled in the fixtureprior to stacking the plates therein to avoid redundant hole drilling.

Fixture 200 retains metal plates 208 in a fixed position so that eachplate may be identically cut by the EDM wire saw cutting wire 210.Drilled and cut in the fixture, all of plates 208 have the same drilledhole position and wire saw cut aperture pattern.

The aperture pattern 212, indicated in dashed lines on plate 208, has apre-drilled hole 214 through which cutting wire 210 is inserted. A highvoltage is placed upon wire 210 with the fixture being grounded. A sparkgap is created by the potential differential between cutting wire 210and fixture 200. The cutting action of the spark gap results inprecision cutting of the pattern. The fixture when placed upon anumerically controlled table under computer control provides precisepattern cutting of the aperture pattern 212. Plate alignment holes suchas hole 216 and mounting holes 218 may be formed either by drilling thehole directly or by drilling a pilot hole and cutting the hole to sizeby using the wire saw.

In the alternative, the back plates, cover shims and air channel shimsmay all be fabricated using chemical milling techniques. FIG. 11illustrates in FIGS. 11A-11F the processing steps in fabricating an airchannel shim like that of air channel shims 32 and 34 of FIGS. 2-7. InFIG. 11A, a piece of 0.012 inch thick berylium copper (Be Cu) shim stock300 is provided for the fabrication of an air channel shim. Shim stock300 is illustrated in a sectional view which corresponds to the viewalong line 7--7 of FIG. 7 when completely fabricated. Shim stock 300 hassubstantially parallel, flat top and bottom surfaces, respectivelysurfaces 302 and 304.

Shim stock 300 is prepared by brushing surfaces 302 and 304 with a finebrass brush. Shim stock 300 is then dipped into a commonly availablecopper cleaning solution to remove contamination and particulates fromthe surfaces. For example, a preferred copper cleaner is thatmanufactured by KEPRO Company of Fenton, Mo. under the part #CU-3. Afterimmersion in the copper cleaner, shim stock 300 is removed and rinsed inwater and dried at 140° F. for 10 minutes.

After drying, shim stock 300 is laminated on surfaces 302 and 304 withphotoresist layers 306 and 308. Photoresist layers 306 and 308 aretypically a thick, dry film thermoplastic polymer photoresist having athickness of approximately 0.001 inches. One such photoresist is thenegative acting photoresist manufactured by KEPRO under part #DFR-3010.Layers 306 and 308 are rolled on with hot rollers at a temperature of300° F. and at a pressure of 20 PSI so as to assure good adhesion of thephotoresist to surfaces 302 and 304. Shim stock 300 with layers 306 and308 laminated thereon is then allowed to cure at room temperature forapproximately 15 minutes.

As illustrated in FIGS. 11B, the 0.001 inch thick mylar film typicallycarried upon the outer surfaces of the stock photoresist is removed. Theremoval of the mylar film allows a photomask to contact the photoresistdirectly. Direct contact of a photoresist mask enables a finer patterndefinition to be achieved in the exposure of the photoresist toultraviolet (UV) light. The artwork for exposure of layers 306 and 308,for the particular finished component, is duplicated so that twoidentical photomasks are generated.

Referring to FIG. 11C, photomasks 314 and 316 respectively placed uponthe respective outer surfaces 310 and 312 of photoresist layers 306 and308. Photomasks 314 and 316 contain transparent and opaque sectionswhich form an exposure pattern in layers 306 and 308 upon exposure ofthe layers to UV light. It should be noted that double-sided processingprovides more precise etching of the holes and air channel apertures inshim stock 300 than does single level processing. However, single levelprocessing in certain applications may achieve acceptable results.

For double-sided processing of shim stock 300, special attention must betaken in that the transparent and opaque patterns of photomasks 314 and316 are accurately aligned. The two masks may be aligned over each otherusing a microscope and then bonded at one edge to spacer 318. In theexample illustrated in FIG. 11C, spacer 318 is of a thickness of 0.014inches with the aligned photomasks 314 and 316 accurately aligned inposition upon the respective photoresist layers 306 and 308. It shouldalso be noted that the air channel aperture formed in a finished airchannel shim must be accurate laid out for the particular application.

Due to the lack of precise control in chemical etching processes, theopaque areas of photomask 314 and 316, which overlie the air channelaperture, are 0.010 inches less in width than the width of the airchannel aperture in the desired end product. The narrow opaque patterncompensates for the uncontrolled lateral etching of the etching solutionas it etches longitudinally through the thickness of the shim.

The photomask covered assembly is then exposed to UV light with theopaque areas, areas 320 and 322 of photomask 314 and areas 324 and 326of photomask 316, blocking the transmission of UV light to theunderlying respective photoresist layer. However, the transparent areas,areas 328, 330 and 332 of photomask 314 and areas 334, 336 and 338 ofphotomask 316, permit UV light to pass therethrough and cure therespective underlying areas in the photoresist layers. The preferredphotoresist material is typically exposed to approximately 60millijoules of ultraviolet light for approximately (40) seconds.

Photomasks 314 and 316, along with spacer 318, are removed. Shim stock300, carrying photoresist layers 306 and 308 respectively upon surfaces302 and 304, is then baked at 140° F. for about 10 minutes.

Photoresist layers 306 and 308 are then developed by placing thephotoresist material laminated shim stock in a spray developing tankcontaining an alkali solution, such as soda ash, as the developer. Onesuch developer is made by KEPRO Company manufacturered under the part#DFD-12G which is a sodium carbonate based developer. This developer isdissolved in water and heated to approximately 104° F. prior to usage indevelopment of the photoresist layers. The photoresist layers are thendeveloped by spraying the heated developer upon layers 306 and 308. Theareas of photoresist layer 306 and 308 which were not struck by the UVlight because they were beneath the opaque areas of the photomasks, aresoluble in sodium carbonate. Therefore, these areas are dissolved by thedeveloper and are removed from the surfaces of shim stock 300.

Exposure of the photoresist layers to UV light in areas beneath thetransparent areas of the photomasks make these areas insoluble to thedeveloper solution. Exposure of the negative photoresist to UV lightcauses the photoresist layer polymers to crosslink thereby increasingthe molecular weight of the material. Therefore, these light struck orcured areas are resistant to removal by sodium carbonate in thedevelopment phase. The light struck portions of photoresist layer 306,areas 340, 342 and 344, respectively located beneath transparent areas328, 330 and 332 of photomask 314, remain upon surface 302 of shim stock300 after spraying of the developer upon photoresist layer 306.Similarly, the light struck portions of photoresist layer 308, areas346, 348 and 350 of layer 308, respectively located beneath areas 334,336, and 338 of photomask 316 remain upon surface 304 of shim stock 300after spraying of the developer upon photoresist layer 308.

FIG. 11D illustrates the post development areas of photoresist layer 306with areas 340, 342 and 344 remaining on surface 302 of shim stock 300.Similarly, on surface 304 the post development areas of photoresistlayer 308, with areas 346, 348 and 350 remaining on surface 304 of shimstock 300. Therefore, with the uncured areas of photoresist layers 306and 308 removed by development, surfaces 302 and 304 are exposedaccording to the pattern defined by photomasks 314 and 316. Thedeveloped assembly is then rinsed with water, dried and inspected forflaws in the remaining photoresist layers. Breaks or pinholes in theremaining photoresist areas are filled with commonly well knownphotoresist pen.

At this stage, shim stock 300 is ready for chemical etching. Shim stock300 is placed in a spray etching tank containing a solution of ferricchloride (FeCl) which is heated to a temperature of 104° F. For the shimstock 300, as described herein, the total etching time is approximatelyone minute. However, the part should be checked approximately everytwenty seconds to determine when the air channel aperture is fullyetched.

FIG. 11E illustrates etched shim stock 300 with the cured sections ofphotoresist layers 306 and 308, areas 340, 342, 344, 346, 348 and 350still remaining upon the surfaces 302 and 304 after etching. Theaforementioned areas are resistant to removal or dissolving by theferric chloride solution which only attacks the exposed metal surfacesof shim stock 300. In FIG. 11E the ferric chloride solution has etchedair channel aperture 352 and hole 354 of the desired size and shape inshim stock 300. It should be noted that the etching occurs from bothsurfaces of shim stock 300 to provide greater resolution in the etchingof the aperture and hole in thick shim stock.

Upon completion of the etching stage, shim stock 300 and the remainingareas of photoresist layers 306 and 308 are rinsed with water. Theremaining areas of photoresist layers 306 and 308 are stripped offusing-a heated potassium hydroxide based photoresist stripper solution.One such photoresist stripper commonly used is that sold by KEPROCompany under the part #DFS-126G that is maintained at a temperature of104° F. for stripping.

Etched shim stock 300 with the cured photoresist removed, is rinsed offin water and dried. The manufactured shim stock is illustrated in FIG.11F. The completed etched shim stock 300 forms an air channel shim suchas air channel shim 32 that is described in its application withreference to FIGS. 2-7. Although single sided etching is possible informing the shims and back plates, higher resolution and faster etchingis achieved when double sided etching processes are used.

Referring to FIG. 12, there is shown, in a series of illustrations12A-12B, the processing of an integrated air channel shim, cover shim,and backplate by using electroforming techniques. The implementation ofthe below described photolithography and electroforming techniquespermits high resolution, precision fabrication of the millimeter wavecircuit board housing in mass quantities. FIG. 12A illustrates a metalbase 400 having a substantially planar top surface 402. Base 400 may beof a metal such as stainless steel or any ocher type of metalconventionally used in permanent, or reusable, electroforming mandrelapplications.

FIG. 12B illustrates a layer of photopolymer in the form of photoresistlayer 404, such as a thin film photoresist sold under the trade name"Riston type 218", applied to surface 402. The thickness of photoresistlayer 404 can be built up by applying multiple layers of the "Ristontype 218" photoresist which is typically 0.002 inches thick. Thethickness of the photoresist layer can be built up to at least 0.012inches by laminating six layers of the "Riston type 218" photoresist onsurface 402. In an alternative and preferred mode, a thick filmphotoresist such as a viscous liquid photopolymer, may be applied tosurface 402 as layer 404. The liquid photopolymer may be leveled offwith a "doctor blade" or by precision machining after drying to achievethe desired thickness. One type of thick film resist which can be usedto generate thicknesses in the range of 0.001-0.080 inches is the"FANTON" series photoresist. The "FANTON" series photoresist is asolvent processable photopolymer resist sold by Armstrong WorldIndustries, Inc. of Lancaster, Pa. Both the "FANTON" and "Riston type218" photoresists are negative resists. Therefore, the polymercross-links and increases its molecular weight so as to becomeimpervious to organic solvents when exposed to ultraviolet light.

FIG. 12C illustrates a photomask 406 placed upon photoresist layer 404.Photomask 406 contains a predetermined pattern of transparent areas 408,410, 412 and 414 and opaque areas 416, 418, 420, 422 and 424. Areas408-424 on mask 406 define a pattern which determines the photoresistareas remaining on base 400 upon subsequent exposure to UV light anddevelopment.

When using the photoresist it is generally required to "soft-bake" thephotoresist after application to remove solvents in the photoresistlayer. With resists such as the "FANTON" series, generally a soft-bakeis required when using the series "100" and "105" photoresist.Typically, for thicknesses of approximately 0.010 inches thick, a twohour bake at 75° F. is followed by a two hour bake at 130° F.

FIG. 12D illustrates the application of UV light to photomask 106. UVlight is transmitted through the photomask transparent areas 408, 410,412, and 414 to underlying areas in photoresist layer 404, areas 428,430, 432 and 434. The UV light is absorbed by the opaque areas 416, 418,420, 422 and 424 in mask 406 such that the underlying areas ofphotoresist layer 404, areas 436, 438, 440, 442 and 444, are notexposed. The "FANTON" series photoresists are preferably exposed to UVlight from conventional mercury-vapor and xenon type light sources forproper curing. However, optimum exposure time depends upon the lightsource employed, the ultraviolet light intensity and the distancebetween the light source and the photoresist layer. For example, a 0.010thickness "FANTON" photoresist layer would require a UV light intensityof 0.125 joules for an exposure time of 45 seconds.

After exposure to UV light, the resist is developed. Photomask 406 isremoved and the areas of photoresist layer 404 unexposed to the UVlight, areas 436, 438, 440, 442 and 444 ace removed by development.Development is done with a chlorinated organic solvent, 1-1-1trichloroethane, at temperatures of 65°-80° F. in a vented tray, aconveyorized spray system or an ultrasonic cleaner operating at 25 KhZ.After removal of the unexposed areas, the photoresist carrying base iswashed with clean 1-1-1 trichloroethane. The base is then sprayed withwater.

FIG. 12E illustrates the post-development stage where only the exposedportions of photoresist layer 404, areas 428, 430, 432, and 434 remainon surface 402. The removal of the unexposed areas or portion formdepressions between adjacent remaining exposed portions. The exposedportions have side walls which define the depressions with the bottom ofeach depression defined by surface 402. Each remaining exposed portionor area on base 400 has a top surface. The structure formed by base 400and the remaining exposed portions of photoresist layer 404 on surface402 forms a photogenerated mandrel which then may be electroplated.

If base 400 is manufactured of a conductive metal other than stainlesssteel, which has a natural passivation film on its surface which canserve as a separation coating, a special coating such as a nickel orchromium plate, or a tungsten disulfide or titanium nitride coat orother separating coating must be placed on the surface. The applicationof this separation coating is preferably done before the photoresist isapplied to the base.

To electroform the device, the photogenerated mandrel (base withphotoresist pattern) is next made electrically conductive by depositingon its surface a thin film of metal such as silver, copper or nickel byan "electroless plating" (chemical reduction) process. These proceduresare well known to those skilled in the art of plating on plastics andsimilar electrical non-conductors. The simplest method suitable for thisapplication consists of immersing the work in a stannous chloridesolution followed by rinsing in water. After this "sensitization" step,the work is immersed in, or sprayed with, a solution of a silver complexwith a reducing agent. This will deposit a thin film of silver over theworkpiece. A further alternative is to paint or spray directly upon themandrel, conductive metallic paints or lacquers based on silver, copper,graphite or other metals or combinations thereof.

The mandrel structure is next immersed in an electroforming bath andplated so as to form thereupon a layer of plating 448 which form thedevice housing. The plated electroformed structure upon the mandrel isillustrated in FIG. 12F.

FIG. 12G illustrates the electroformed housing 450 as removed from base400 by prying or lifting. The cured photoresist areas 428, 430, 432 and434 and are then removed by a photoresist stripping process. Strippingmay be accomplished by soaking the structure in a hot resist strippersuch as methylene chloride. The stripping is also accompanied withagitation or brushing to remove the remaining cured photoresistmaterial.

FIG. 12H illustrates the completed electroformed housing 450. Theregions in which the cured photoresist is removed forms preciselydimensioned regions which define interior cavities for components andair channel apertures. The surfaces of areas 428, 430, 432 and 434 havebeen utilized to form dimensionally precise interior cavities and airchannel apertures of the electroformed housing. These cavity and airchannel aperture regions are as illustrated as regions 452, 454, 456 and458. In essence, the top and side surfaces of the cured photoresist andthe exposed portions of surface 402 has formed dimensionally precise airchannel apertures and component placement cavities. Structure 450 thenmay be drilled or further processed for mounting in conjunctiontherewith an appropriately designed circuit board with circuit patternsformed thereupon for exact registration within the housing.

Using the just described technique, it is envisioned that multiplehousings may be electroformed on a single base plate. Therefore, timeand cost savings may be realized in fabrication of large quantities ofhousings.

FIG. 13 illustrates supplemental steps in the forming of the mandrelused to fabricate an electoformed device housing. These supplementalsteps enable wherein multiple level structures to be formed.

FIG. 13A illustrates base 460 as having formed upon surface 462photoresist layer 464. Photomask 466 is placed upon surface 465 ofphotoresist layer 464. Photomask 466 contains transparent areas 468,470, 472 and 474 and opaque areas 476, 478, 480, 482 and 484. Uponexposure to UV light, the areas in photoresist layer 464 beneath thetransparent areas of photomask 466, areas 486, 488, 490 and 10 492become insoluble to organic solvents as previously discussed. However,the areas in photoresist layer 464 beneath opaque areas of photomask 466areas 494, 496, 498, 500 and 502, are uncured and susceptible to removalby organic solvents also as previously discussed.

After exposure to UV light, photomask 466 is removed. Upon removal ofphotomask 466 an additional photoresist layer 504 of a desired thicknessis deposited upon surface 465 of photoresist layer 464. Photomask 506 isplaced upon top surface 505 of layer 504. Photomask 506 also containstransparent sections, sections 508 and 510, and opaque sections,sections 512, 514 and 516. The transparent sections physically overlieareas in photoresist layer 464 which were previously exposed to UVlight.

Upon exposure to UV light, the areas in layer 504 beneath photomasktransparent sections 508 and 510, respectively areas 518 and 520 arecured and become impervious to organic solvents. However, the areas inlayer 504 beneath photomask opaque areas 512, 514 and 516, respectivelyareas 522, 524 and 526, are unexposed to UV light and are thereforesusceptible to removal by organic solvents.

Referring to FIG. 13C, photomask 506 has been removed and the uncuredareas of layers 504 and 464 are removed by techniques discussed earlier.As a result areas 486 and 488 in photoresist layer 646 and the combinedareas of 490 and 518, respectively of photoresists layers 464 and 504,along with combined areas 492 and 520, respectively of layers 464 and504 remain. These areas of cured photoresist form depressions whichextend downwardly to surface 462 of base 460. Depression 528 is definedby the sidewalls 538 which extends from surface 465 of area 486 tosurface 462. Depressions 530 is defined by surface 462 and sidewalls 540and 542 which respectively extend from surface 465 of areas 486 and 488.Depression 532 is defined by surface 462, and sidewall 544 which extendsfrom surface 465 of area 488 to surface 462. At the other side ofdepression 532, the depression is defined by the combined structure ofareas 498 and 518. The other sidewall of depression 532 formed bysidewall 546 which extends from surface 505 of area 518 downwardly tosurface 465 of area 490. The other sidewall is further defined bysurface 465 and sidewall 548 which extends from surface 46 5 downwardlyto surface 462. Depression 534 and 536 are similarly defined as wasdescribed with reference to depressions 528, 530 and 532.

The photogenerated mandrel structure as defined by base 460 and thedeveloped layers 464 and 504 is then processed in a manner as previouslydescribed with reference to FIGS. 12E-12H. The resulting structureformed by the mandrel permits a multi-level electroformed housing 550 tobe fabricated as illustrated in FIG. 13D. Similarly, as was described inFIG. 12, the cured portions of photoresist layers 464 and 504 definecavities 552, 554, 556 and 558 which provide precise dimensioning ofinterior cavities and apertures.

FIG. 14 illustrates yet another embodiment of the integrally formed backplate and thick photoresist pattern wherein the photoresist layer isused to confine the electrodeposition pattern rather than serve as anelectroforming mandrel. By this procedure a permanent metalelectroforming mandrel is fabricated. In FIG. 14A, a processedphotoresist pattern is formed in photoresist layer 600 on surface 602 ofbase 604. The mechanism by which the layer 600 was deposited and formed,with resulting exposed areas 606, 608, 610, 612 and 614, is previouslydiscussed with reference to FIGS. 12 and 13.

After developing the patterned photoresist layer on the base surface602, the depressions formed between the remaining areas of photoresistlayer 600, areas 606, 608, 610, 612 and 614, are filled by metaldeposited in an electroforming bath process. FIG. 14B illustrates thedeposition of metal area 616 confined within the sidewalls of area 606and 608 and base surface 602. Similarly, sections 618, 620 and 624 arerespectively formed between the sidewalls of areas 608 and 610, areas610 and 612, and areas 612 and 614.

Due to the lack of precise control of the rate of depositing metal onsurface 602, an uneven top surface results in sections 616, 618, 620 and624. Therefore, the top surface must be machined down to a predeterminedprecision height, A, above surface 602. The machining of the section topsurface gives a flat top surface to each of sections 616, 618, 620 and624. FIG. 14C illustrates the machined top surfaces of the depositedsections.

Photoresist layer 602 is then removed such that only sections 616, 618,620 and 624 remain on base 604. In an alternative step, as illustratedin FIG. 14D, the photoresist is removed prior to the precision machiningof the dimension A to form the top surface of sections 616, 618, 620 and624. FIG. 14D illustrates the electroformed mandrel with photoresistlayer 600 removed prior to machining of the top surface of theelectrodeposited metallic sections.

FIG. 14E illustrates the machined mandrel whether formed as withreference to FIG. 14C or FIG. 14D. In either case, photoresist layer 600is removed and the top surface of each section is precision machined apredetermined height above base surface 602. Section 616, 618, 620 and624 in combination with base 604 comprise the electroforming mandrelupon which the housing is then electroformed.

FIG. 14F illustrates a separation coating 626 (exaggerated thickness)formed on the exterior surfaces of section 616, 618, 620 and 624 and theexposed portion of surface 602. This separation coating permitsseparation of an electroformed housing from surface 602 and sections616, 618, 620 and 624. Upon forming the separation coating such astungsten disulfide, titanium nitride, chromium or nickel on surface 602and the surfaces of the sections, the mandrel is immersed in anelectroforming bath. An electroformed housing 630 is then formed overthe mandrel.

FIG. 14G illustrates electroformed housing 630 as removed from base 604and sections 616, 618, 620 and 624. Electroformed housing 630 is removedby prying such that it separates from the mandrel with the sectionsremaining on the mandrel base. Housing 630 is therefore formed withcavities 632, 634, 636 and 638 being respectively defined by thesurfaces and sidewalls of sections 616, 618, 620 and 624.

FIG. 15A illustrates a conventionally machined metal mandrel 650 with abase portion 652 upon which sections, sections 654, 656, 658 and 660extend above a top surface 662 of base portion 652. FIG. 15B illustratesmandrel 650 with an electroformed housing 664 formed thereupon asdiscussed with reference to FIGS. 12-14. In cases where a metal mandrelother than stainless steel is implemented, a special separation layer(not shown) must be placed upon the mandrel prior to immersion in theelectroforming bath as previously discussed. The separation layerpermits easy removal of electroformed housing 664 from mandrel 650. Thehousing as removed from mandrel 650 is illustrated in FIG. 15C. In FIG.15C, cavities 666, 668, 670 and 672 are respectively defined by the topsurfaces and sidewalls of section 654, 656, 658 and 660.

In any of the processing techniques utilized in fabricating theintegrated housing, multiple housings may be formed upon a single baseto permit large volume, high quality fabrication. Implementation ofthese techniques enables the realization of low cost, high precision,mass produced millimeter wave devices.

The previous description of the preferred embodiments are provided toenable any person skilled in the art to make or use the presentinvention. Various modification to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without the use of theinventive faculty. Thus, the present invention is not intended to belimited to the embodiment shown herein, but is to be accorded the widestscope consistent with the principles and novel features disclosedherein.

What is claimed is:
 1. A method of fabricating a millimeter wave devicehousing plate, comprising the steps of:providing a metallic plate of athickness between 0.1 and 0.2 inches, having substantially flat paralleltop and bottom surfaces and four side edges forming a rectilinear outerperiphery to said plate, placing a layer of photoresist material uponeach of said top and bottom surfaces, placing a mask, having apredetermined transparent and opaque pattern formed therein, adjacenteach photoresist layer, the masks having identical transparent andopaque patterns, aligning the masks so that their patterns areaccurately aligned, securing the aligned masks together along one sideedge of the plate, providing ultraviolet light to said masks, saidultraviolet light passing through said mask transparent patterns intosaid photoresist layers, removing said masks from each photoresistlayer, developing each photoresist layer so to remove ultraviolet lightunexposed portions of each photoresist layer present from said top andbottom surfaces and expose portions of underlying correspondingsurfaces, and etching said metallic plate at said exposed portions ofboth of said underlying corresponding surfaces to form predeterminedapertures through the plate.
 2. The method as claimed in claim 1,wherein said etching step comprises spray etching.
 3. The method ofclaim 2 wherein said step of spray etching said metallic plate comprisesthe steps of:spraying a metal etching solution upon said plate at eachsurface of said plate having said exposed portions of said metallicplate, removing etched metal and said etching solution from said plate;and removing said ultraviolet light exposed portions of each photoresistlayer.
 4. The method as claimed in claim 1, wherein the masks each havea projecting portion which project outwardly from said one side edge ofsaid plate, and the steps of aligning and securing the aligned maskstogether comprise placing a spacer along said one side edge of the mask,the spacer having an upper face aligned with the photoresist layerplaced on said top surface of said plate and a lower face aligned withthe photoresist layer placed on said bottom surface of said plate,placing said masks in alignment with said projecting portions of saidmasks projecting over the upper and lower face of said spacer,respectively, and bonding said projecting portions to the respectiveupper and lower faces of said spacer when said masks are in alignment.5. The method as claimed in claim 1, wherein the photoresist material isa dry chemical photoresist and a plastic film coating on both faces ofthe photoresist material is removed prior to placing a layer of thephotoresist material on each of said top and bottom surfaces, and themasks are placed in direct contact with the dry chemical photoresistmaterial.
 6. A method of fabricating a millimeter wave device housingplate, comprising the steps of:providing a metallic plate of a thicknessbetween 0.1 and 0.2 inches, having substantially flat parallel top andbottom surfaces and four side edges forming a rectilinear outerperiphery to said plate, placing a layer of photoresist material ofuniform thickness upon each of said top and bottom surfaces, placing afirst mask, having predetermined transparent and opaque patterns formedtherein, adjacent one of said photoresist layers and placing a secondmask having identical patterns against the other photoresist layer withthe patterns in alignment, securing the masks together along one sideedge of said plate, providing ultraviolet light to said masks, saidultraviolet light passing through said mask transparent patterns toexpose predetermined portions of each photoresist layer to ultravioletlight, removing said masks from each photoresist layer, spraying solventupon each photoresist layer so as to dissolve portions in eachphotoresist layer unexposed to ultraviolet light, rinsing eachphotoresist layer so as to remove dissolved photoresist material fromeach photoresist layer on said plate, and etching said metallic plate atthe remaining exposed portions of each photoresist layer.